adding an extra channel?

would it be possible to add an extra channel to my bass amp? for example, an overdrive preamp? are there any brands of preamps or rackmount effects that can do that? The problem is, i don't know how to get total bass distortion (no clean signal) running through my effects loop, which is mixed because it sounds 3x better that way. A preamp with a footswitch would be a great help.